page_title: San Jacinto Fault Zone
section_title: San Bernardino Valley
hierarchical_section_title: San Jacinto Fault Zone / Characteristics / Segments / San Bernardino Valley
caption_attribution_description: English: The Southern California Coast, from San Pedro Bay (Los Angeles) to San Diego Bay, with the Peninsular Ranges. Taken in 2008.
context_page_description: The San Jacinto Fault Zone is a major strike-slip fault zone that runs through San Bernardino, Riverside, San Diego, and Imperial Counties in Southern California. The SJFZ is a component of the larger San Andreas transform system and is considered to be the most seismically active fault zone in the area. Together they relieve the majority of the stress between the Pacific and North American tectonic plates.
  The SJFZ itself consists of many individual fault segments, some of which have only been individualized as recently as the 1980s, but activity along the line of faults has been documented since the 1890s. One segment of the SJFZ, the Anza seismic gap, has not experienced any major activity since instrumental records have been kept. Each segment was evaluated for its seismic risk and was assigned a probability for the occurrence of a large rupture for the thirty-year period starting in 1995.
  While several of the large earthquakes along the SJFZ have not resulted in significant property damage or loss of life the cities of Hemet and San Jacinto were both heavily damaged in two significant events in 1899 and 1918.
context_section_description: The northernmost primary strand of the SJFZ is the Claremont strand (though subsidiary parallel strands exist). It spans a total of 75 km (47 mi), from its northern endpoint in Cajon Pass to its southern endpoint in the San Jacinto Valley. Within the San Bernardino Valley itself, the SJFZ approaches or intersects the right-lateral strike-slip San Andreas Fault to the north, the oblique normal Crafton Hills Fault Zone to the east, and the Cucamonga Thrust to the west. A series of moderate earthquakes affected this area in the 1890s, though it is uncertain how many of these occurred specifically on the SJFZ. The Claremont strand has not had a major earthquake in the instrumental period, but paleoseismology indicates that its last surface rupturing event occurred in the early 19th century, and that comparable earthquakes occur on average of every 160 to 220 years.
caption: California Coast, Los Angeles to San Diego Bay. Overlaid lines on this  NASA photo (2008) identify the San Jacinto Fault Zone (right) parallel to the Elsinore Fault (left)
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